Sandwich Tern

I saw a sandwich tern for the second time in the Sado Estuary of Portugal while riding the ferry from the Troia Peninsula to Setubal. 

I'd previously seen it on the Padre Island National Seashore outside Corpus Christi, Texas. 

It has a thin sharp black bill with a yellowish tip that can be difficult to see. It has black legs, grayish upperparts, white underparts and a shaggy black crest during breeding. In non-breeding, the black crest just covers the back of he head, giving it a bald appearance on the top, like an aging rocker with long hair.

Sandwich tern range, from Wikipedia.